U.S. Pat. No. 5,325,673 publication describes a method of pre-treating a natural gas stream for liquefaction by removing heavier hydrocarbons from it, comprising the steps of:    a) introducing a natural gas feed stream into a scrub column having upper enriching and lower stripping sections;    b) contacting the feed stream with a liquid reflux stream introduced into the upper enriching section of the column to absorb C5+ hydrocarbons from the feed stream;    c) recovering an overhead vapour product containing C2–C4 hydrocarbons and having a concentration of less than about 1 ppm C6+ hydrocarbons;    d) reboiling a portion of liquid in the lower section of the column to strip lighter hydrocarbons from the feed stream;    e) recovering a liquid bottom product enriched in C5+ hydrocarbons; and    f) operating the column to obtain the C2–C4 hydrocarbons primarily in the overhead product.
The process is directed to obtaining an overhead product that has a very low concentration of C6+ hydrocarbons. However, the overhead product still contains considerable amounts of ethane, propane and butanes.